This invention relates to a cathode ray tube of the type in which a separate front panel is bonded to the display face of the tube. The purpose of the panel is to reduce glare, to enhance contrast and to reduce the danger of injury from shattering glass in the event the tube implodes.
In one known method for securing a panel to the tube, the panel is held so as to be spaced a predetermined distance (e.g., 1/16" to 1/4") forwardly from the display face of the tube. A strip of pressure-sensitive tape then is wrapped around the outer peripheries of the tube and the panel to enclose the gap therearound and to cause a closed cell to be defined between the tube and the panel. Thereafter, a clear bonding agent such as polyester resin is injected into the cell and is allowed to cure in order to cement the panel rigidly to the tube. It is necessary to provide vent holes or the like in the tape to allow air to escape from the cell during injection of the resin.
It is important that the spacing between the panel and the tube be uniform across the full area of the panel during curing of the resin. If the spacing is not uniform, the cured resin will be of non-uniform thickness, will undergo differential thermal expansion and contraction, and will cause the panel to separate from the tube.
In the past, there have been a number of ways for establishing the spacing between the panel and the tube prior to application of the tape. For example, the panel may be held in spaced relationship with the tube by a pair of rods placed between the panel and the tube while three sides of the panel are taped, the rods being removed prior to taping of the fourth side. When the fourth side is taped, care must be taken to avoid tilting the panel and changing the spacing.
A second method of spacing involves the placing of four spacer blocks of previously cured resin between the panel and the tube at the corners of the panel. The spacer blocks remain in place permanently and, in some cases, are objectionable from a visual standpoint.
With yet another method of spacing, the panel is fixtured in vacuum cups and is held a predetermined distance from the tube as the tape is applied.